1. Field of the Invention
The present invention relates to a video encoder, and relates, more particularly, to a video encoder using a so-called bit-rate control for controlling the number of output bits to become a constant volume during a predetermined period of time.
2. Description of the Related Art
As one of conventional systems of a video encoder for controlling the number of output bits to be a constant volume during a predetermined period of time, there has been proposed a system that controls the number of output bits by only changing the quantizing level based on fixed constant time interval for input images that are processed (a first conventional system).
As another control system, there has been proposed a method for achieving uniform picture quality as a whole by controlling in advance the number of output bits to be generated in the future based on pre-obtained information on images which are ahead of images currently being processed (a second conventional system).
According to the above-described first conventional method, however, as the time interval for input images to be processed is fixed at a constant rate, it is only possible to allocate an almost uniform volume of bits both to images that do not require much information and to images that require much information in video encoding. Accordingly, it is not possible to make uniform the overall picture quality as allocation of the number of bits is not performed according to the complexity from an encoding point of view.
Further, according to the above-described second conventional system, as the number of bits are controlled by utilizing image information to be processed in the future, there occurs a processing delay without an exception in the case of processing images by placing a weight on realtime processing. Accordingly, it is difficult to apply this method to a processing that attaches a great importance to realtime processing.
It is an object of the present invention to provide a video encoder that can make it possible to make uniform the overall picture quality in the case where input video images change greatly due to motion or the like during a certain period of time and in the case where image features vary suddenly due to a scene change or the like. It is another object of the present invention to provide a video encoder that can perform video encoding with uniform picture quality without using future image information, that is, a video encoder that can perform a video encoding with uniform picture quality based on a realtime processing.
In order to achieve the above objects, according to a first aspect of the invention, there is provided a video encoder using a rate control for controlling the number of output bits to become constant during a certain period of time, wherein the video encoder includes: means for specifying a time at which an input image to be processed next is to be input after finishing an image encoding, based on at least a variance of the number of output bits of an input image from a scheduled number of output bits, a skip time interval between processed images previously detected from a video picture, and a virtual buffer status of an encoded information virtual storage for temporarily storing an encoded signal for transmission; and means for deciding whether or not an input image to be processed next selected based on the time specification is an image to be processed [or not] from an image variance between the input image and an image processed immediately before.
According to the above-described aspect of the invention, it becomes possible to make variable the time interval between video images to be encoded and it also becomes possible to change a video input image to be encoded from pixel information of the image to be processed, thereby making it possible to encode video images without losing a realtime processing feature.
Further, according to a second aspect of the invention, there is provided a video encoder for dividing the selected image to be processed into a plurality of small areas, with a target number of output bits set for each small area, and for determining quantizing levels of small areas to be sequentially encoded next based on the target number of output bits for each small area and the actual number of output bits of each small area sequentially encoded.
According to this aspect, it becomes possible to achieve uniform picture quality of the encoded video images.